He said while the delays were disappointing, the Government had been "riding John Holland very hard" to keep on top of the delays.

It would then take about five months to commission and fit out the hospital ready for patients, which would blow out the opening date to next spring or summer.

"We're not being specific, we're just saying the second half of the year so that we're not messing people around because if there's any further delays in construction, but as I say, we're dependant on them [John Holland] finishing," Dr Hames said.

He said the builder had experienced problems sourcing equipment, but admitted the Government had altered the hospital's plans.

"There are penalties for being late, but that depends on how much of the lateness is their fault and how much is from changes we've made to commissioning along the way," he said.

"There's been some change to requirements for construction along the way - we added an extra 24 beds during the process of design."

Opposition Health spokesman Roger Cook said the Government could have avoided the delays.

"We have a suspicion that the delays at the new children's hospital are as a result of the Barnett Government continuing to fiddle at the edges with the configuration as they try to respond to the very real criticism that the hospital will be too small by the time it opens," Dr Cook said.

"The Barnett Government has been trying to retrofit a whole range of facilities of that hospital where really what they should have done is better plan the hospital with extra capacity, including and extra floor to meet the needs of a growing Perth population."

Timing less important than getting it right: AMA

The Australian Medical Association said it was disappointed the hospital's opening had been delayed.

However, WA branch president Michael Gannon said he was pleased children would not be moved into the new hospital during winter.

"I think we've given them the appropriate advice that winter is no time to be moving the sickest children in our community," Dr Gannon said.

"They listened on this occasion, we really wish they'd listen a bit more often.

"It's so much more important that they get it right than worry about when it's opening."

Dr Gannon said little money had been spent on Princess Margaret Hospital and if the hospital was to stay open another year, the Government would need to address issues as they arose.

"One of the concerns is, for understandable reasons, they haven't spent a cent on Princess Margaret Hospital for a long period of time now and that's an aging facility that will probably be left with not a lot of money spent on it for another six months."